AbstractThe neutron noise was formulated based on a multidimensional, multiregion, multigroup diffusion model. To solve for the flux fluctuations, the model was generalized and clarified using the adjoint function approach, which included checking the reciprocity relation to assure the correctness of the established adjoint function, solving the adjoint function with a finite-volume detector, and increasing the rate of convergence of the series solutions by nonlinear transform.The model was applied to a coupled core reactor to recalculate detector responses to a unidirectional vibration of a neutron absorber. The lack of agreement between the calculated results and the measurements might be partly due to some simplifications and approximations. It is recommended that measurements should be made in cases where the model can be used more feasibly.